1. Field of the Invention
The present invention relates to a system and method for reducing or eliminating condensation associated with exhaust gas recirculation (EGR) for an internal combustion engine.
2. Background Art
A number of strategies have been developed for alternative charge air handling and turbocharging to drive and control exhaust gas recirculation (EGR) to reduce emissions for truck, automotive, and stationary engines used in power plants. One approach uses a variable geometry turbocharger (VGT), in combination with an EGR circuit to achieve the desired ratio of EGR rate and air/fuel ratio under transient and steady-state operation. In this arrangement, the EGR circuit generally includes a modulating (proportional) or on/off EGR valve, an EGR cooler, and an EGR rate measuring device with appropriate tubing or integral passages to direct exhaust gas to the engine intake under appropriate operating conditions. The management of EGR flow is performed by an electronic control unit (ECU). The ECU may use closed loop control of the EGR flow which is dependent on EGR rate measurement. The ECU may also control the VGT and/or EGR valve based on input from the rate measurement device to regulate EGR flow.
Recirculated exhaust gas acts as a dilutant to the charge air, and is used to lower the peak combustion temperature to reduce NOx formation. However, this also lowers the volumetric efficiency of the engine. This leads to a lower (richer) air/fuel ratio in comparison to a non-EGR engine because the recirculated exhaust gas has less oxygen content than the charge air due to the oxygen being consumed during the previous combustion process. For an EGR engine to maintain the same air/fuel ratio as a non-EGR engine under the same operating conditions generally requires an increased turbo boost which may in turn require an increase in back pressure to drive the recirculated exhaust gas.
As described above, NOx formation increases with increasing peak combustion temperatures. As such, NOx formation is directly related to the intake manifold temperature (IMT), which represents the temperature of the compressed intake air downstream of the charge air cooler and the EGR gases. The EGR cooler is used to cool the exhaust gases prior to combining with the charge air to lower the overall IMT and reduce the formation of NOx. However, under some operating and ambient conditions, the EGR cooler can excessively lower the recirculated exhaust gas temperature resulting in acidic condensation, which may lead to premature degradation of various components including the intake manifold and cylinder liner and kits.
The present invention provides a system and method for controlling an internal combustion engine to reduce or eliminate formation of EGR condensate. A representative system and method, in one embodiment of the present invention, monitor current ambient and operating conditions to determine whether conditions are favorable for condensation of EGR gases. When these conditions are detected, the engine is controlled accordingly to avoid condensation. Preferably, the engine is controlled to increase the intake manifold temperature to reduce or eliminate condensation. In one embodiment, the intake manifold temperature is increased by redirecting some or all of the EGR flow to avoid the EGR cooler such that the average EGR gas temperature increases and results in an increase of the intake manifold temperature. Alternatively, or in combination, some or all of the charge air may be redirected to bypass the charge air cooler and/or redirected from the outlet of the turbocharger compressor to the intake, effectively increasing the intake air temperature and resulting in a corresponding increase of the intake manifold temperature.
In one embodiment of the present invention, a method for controlling an internal combustion engine to reduce formation of EGR condensation includes determining current ambient conditions, determining current engine operating parameters, determining a dew point based on the current ambient conditions and engine operating conditions, comparing intake manifold temperature to the dew point, and controlling the engine to avoid condensation if the intake manifold temperature is within a particular range of the dew point. Controlling the engine to avoid condensation may include redirecting some or all of the EGR gas and/or charge air to bypass a corresponding EGR cooler and charge air cooler, respectively.
The present invention provides a number of advantages. For example, the present invention reduces or eliminates the formation of condensation within the intake system so that various engine components are not subjected to corrosive condensate related to use of EGR. The present invention does not require a humidity sensor to detect ambient humidity to avoid condensation and therefore may provide a lower cost, and less complex, strategy for avoiding EGR condensation than some prior art approaches.
In carrying out the above features and advantages of the present invention in addition to various other features and advantages, a system for providing exhaust gas recirculation in a multi-cylinder compression ignition internal combustion engine includes an EGR valve in communication with an exhaust side of the engine to selectively divert a portion of the exhaust through an EGR circuit to an intake side of the engine. An EGR cooler is disposed within the EGR circuit to cool the EGR flow. In one embodiment, a bypass valve is positioned downstream of the EGR valve and upstream of the EGR cooler to selectively divert at least a portion of recirculated exhaust gas around the EGR cooler based on engine and ambient operating conditions to reduce or eliminate condensation of the recirculated exhaust gas. The system may also include a charge air cooler bypass valve used alone or in combination with the EGR bypass valve to selectively bypass the charge air cooler for a portion or all of the charge air from the turbocharger before being mixed with the EGR flow to reduce or eliminate condensation in the intake manifold.
The present invention also includes computer readable storage media having stored instructions executable by a computer to control an internal combustion engine. The instructions include instructions for detecting current engine and ambient operating conditions favorable to formation of condensation, and controlling the EGR bypass valve and/or charge air cooler bypass valve to raise the intake manifold temperature to avoid condensation of EGR gas.
Various advantages and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.